Waveguides are structures used to guide and facilitate the transmission of waves. Waveguides are commonly used in optical applications to channel and propagate light. Waveguides range in complexity from common optical fiber to multilayered semiconductor devices.
One drawback with conventional waveguides is that they do not efficiently couple light. That is, light directed towards a waveguide simply propagates down the waveguide by continually reflecting off the internal surfaces of the waveguide. Inherently, as the light reflects off the surfaces of the waveguide, there is signal loss. Also, the propagation distance may be reduced due to the signal loss.
Moreover, problems arise in the transfer of the light from the light source to the waveguide because the light often passes through another medium, such as air, before it enters the waveguide. To compensate for the aforementioned problems, waveguides and light sources must be fabricated to exacting specifications. The difficult manufacturing process increases the costs of conventional waveguides and light sources.